The present invention is directed to improvements in stator assemblies for brushless DC permanent magnet motors and generators of the type wherein the stator is located internally of a permanent magnet rotor.
Inexpensive, high-production manufacture of the foregoing type of rotary permanent magnet devices has been hampered in the past by difficulties in constructing the stator assembly of the device. Such stator assemblies normally are composed of an annular, magnetically-permeable core upon which an electrically-conductive winding is mounted, with a circuit board spaced axially from the core and winding which feeds electrical power to the winding. The circuit board also mounts Hall effect sensors, which detect the rotational attitude of the rotor's permanent magnets by sensing their magnetic fields and cause commutation of the electrical current to the winding in response to the magnets' positions by means of well-known electronic circuits designed for this purpose.
At present, relatively high manufacturing costs are incurred in the process of precisely and rigidly orienting the core and its associated winding both angularly and axially with respect to the circuit board. Such orientation is critical to enable high-speed automated soldering of the winding leads to the circuit board while avoiding improper wire position and preventing wire fatigue and resultant breaking during manufacture, and also to orient the winding angularly with respect to the Hall effect sensors.
Precise axial orientation of the rotor with respect to the circuit board is also critical, so that the Hall effect sensors on the circuit board are positioned in correct axial proximity to the permanent magnets of the rotor for proper detection of the magnetic fields.
Currently it is a common practice to utilize multiple screws or spacers to interconnect the core and circuit board, after the winding has been mounted on the core, to provide the above-mentioned angular and axial orientation between the core and circuit board. However, the installation of the screws or spacers is time-consuming and expensive, and can also cause damage to the winding if not very carefully performed.
Alternatively it has been known to utilize specially constructed winding bobbins capable of providing the above-mentioned angular and axial orientation functions, as exemplified by U.S. Pat. No. 4,259,603. However, such bobbins provide the orientation features only as an integral part of the structure for mounting the winding, resulting in an extremely complicated stator assembly. Such an arrangement does not permit addition of the orientation features to the core after the winding has been mounted thereon, which would facilitate the process of mounting the winding on the core, as well as simplifying the stator structure.
Accordingly, what is needed is a stator assembly for this type of electrical device which automatically and inexpensively performs all of the foregoing angular and axial orientation functions by means of a member connectable to the core after the winding has been mounted thereon, without the need for precise and time-consuming manipulations.